[Q] Can't flash a boot.img

Hey guys,
Recently i deleted everything in a drunken state, so i flashed Android revolution hd one 71.1 (after a couple of hours) using the htc all in one tool and sideload.
it installed, but now i stuck, cause it keeps booting into recovery (TWRP 2.6.3.0) and every attempt to flash the boot.img via fastboot fails
it says waiting for device all the time...

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